The short-term research objective, as outlined in the current proposal, is to elucidate the cellular mechanisms underlying the action(s) of individual modulators (ie, dopamine) of prolactin secretion. The long-term research objective is to establish a basis for understanding integrated neuroendocrine function during physiological changes in prolactin secretion. Incorporation of a perfusion technique to measure temporal patterns of prolactin secretion and an imaging technique to measure intracellular [Ca2+], will yield greater insights into mechanisms of stimulus-secretion coupling. Prolactin is a pituitary hormone involved in numerous reproductive and nonreproductive processes. Unlike most endocrine cells, which do not secrete unless stimulated, the pituitary lactotrope requires constant inhibition to keep its secretory activity under control. The primary physiological inhibitor of prolactin secretion is dopamine. However, dopamine is involved in a complex interplay with other neurotransmitters and hormones. The dynamics and complexity of this system have been the major impediments to our understanding of the control of prolactin. Consequently, it is necessary to define the mechanisms of action of each of these regulators before we can understand their integrated actions in vivo. Elucidation of these mechanisms will be achieved through the application of diverse experimental approaches (immunology, biochemistry, electrophysiology) in a concerted manner to functionally-defined prolactin-secreting cells. Measurements of the secretory and ionic activity in single lactotropes will provide insights into the basis of their functional heterogeneity, while measurement of prolactin release from populations of cohort cells will provide information on the integrated, temporal profile of their secretory behavior. Prolactin hypersecretion is the major neuroendocrine cause of infertility in women and importance in men. The defect in prolactin-secreting tumors appears to be an intrinsic abnormality of the lactotropes, leading to loss of dopaminergic inhibition. The research proposed herein will provide a framework in which to examine selected aspects of cell function and abnormalities associated with pathologies of prolactin secretion.